1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and apparatus for accessing a cell by a user equipment (UE) in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
User equipments (UEs) may move from a serving cell to a neighbor cell through a cell reselection procedure. Due to movement of UEs, the number of UEs accessing a particular cell may increase to cause overload in the corresponding cell. In order to prevent generation of overload, a wireless communication system provides a scheme of restricting an access. Restriction on UE's access to a particular cell is known as access barring.
Over a cell in which access barring is set, a UE determines whether its access is permitted based on access barring setting, and when not permitted, the UE may attempt to access a neighbor cell. When the UE is permitted to access the neighbor cell or the neighbor cell is not set with access barring, the UE may establish a connection with the corresponding neighbor cell.
In a communication system environment in which a great number of UEs coexist, when a UE access is not permitted due to access barring set for a particular cell, the UE may move to an accessible neighbor cell. In particular, a large number of UEs, which have failed to access due to access barring, may intend to establish a connection to a neighbor cell not set with access barring, which may cause excessive overload in the corresponding cell. Thus, a cell accessing method that may be able to prevent generation of unintentional overload in a particular cell is required.